A solid electrolytic capacitor element is prepared, for example, by electrolytic oxidation of a sintered compact of a valve-action metal powder, such as tantalum, niobium, tungsten or the like, in an aqueous solution of an electrolyte such as phosphoric acid to chemically convert the surface of the sintered compact into a dielectric layer of a metal oxide; electrolytic polymerization to form a semiconductor layer on the dielectric layer; and forming a carbon layer on the semiconductor layer. The carbon layer is usually formed from a carbon paste. For example, the carbon paste as described in Patent Document 1 is a paste composed of carbon particles and catechol or pyrogallol. Patent Document 2 discloses a carbon aqueous solution or a carbon paste prepared by mixing carbon and an aromatic compound having a sulfonic acid group.